1. Field of the Invention
The present invention generally relates to a pressure sensor formed on a semiconductor substrate and, more particularly, to setting a reference voltage in a circuit peripheral to the pressure sensor on the semiconductor substrate.
2. Description of the Prior Art
A pressure sensor formed on a semiconductor substrate generally includes a pressure detecting circuit and a peripheral circuit which compensates for a temperature-dependent change to thereby adjust an output characteristic. This peripheral circuit must extremely faithfully amplify a micro-voltage generated from the pressure detecting circuit as a function of the magnitude of a pressure applied to the pressure sensor. Accordingly, the peripheral circuit generally includes a differential amplifier which may be in the form of, for example, an operational amplifier. In the pressure sensor formed on a semiconductor substrate, the pressure detecting circuit, and a portion of the peripheral circuit such as the operational amplifier, are integrated together on the semiconductor substrate.
Accordingly, when input terminals of the operational amplifier and/or a source of a reference voltage required for differential amplification are to be formed outside an integrated circuit board which includes the pressure detecting circuit and that portion of the peripheral circuit, the reference voltage is generally divided by two resistors connected in series between a power source and ground.
As is well known to those skilled in the art, when the resistors used to set the reference voltage have difficult respective temperature coefficients, the reference voltage will be undesirably affected by, and hence vary, depending on the temperature. Because the pressure sensor formed on the semiconductor substrate, or the semiconductor pressure sensor as referred to hereinafter, requires a pressure signal to be amplified some tens to 200 times by the peripheral circuit, this temperature-dependent change of the reference voltage will be correspondingly amplified, resulting in a detection error in the output of the semiconductor pressure sensor.